Item:big root/expert belt
Big root boosts giga drain's power and makes it more efficient at healing, ice punch for dragon, ground, and flying types, shadow ball for ghosts and other psychics, thunderbolt to handle waters that giga drain can't handle, and extrasensory for poison and fighting types.
Fire punch to handle grass, bug, steel, and ice types.
Thunderpunch is a physical alternative to thunderbolt.
Phychic if you prefer the special defense lowering to the flinch from extrasensory.
Charge beam boosts special attack 50% of the time, good for special attack based sets.
Thunder wave is a good status move for faster opponents.
Yawn/dream eater combo for stab healing.
Signal beam just for coverage on anything you may have missed.
Energy ball is basically a weaker grass type psychic.